Gel electrophoresis is a process that has long been in use for clinical diagnosis and laboratory research. It is based upon the principle that electrically charged biological macromolecules will migrate through a solvent medium when subjected to an electrical field. Since macromolecules may vary in molecular weight and charge, it is possible to use an electrophoresis process to distinguish between different macromolecules based on their respective rates of movement through the solvent. Electrophoresis can also be used for other types of macromolecule analyzation, such as detecting amino acid changes.
In gel electrophoresis, the solvent is cast as a gel and solidifies into a thin planar slab. Originally, the laboratories mixed the gel and cast their own gel slabs on-site, and would inject the biological macromolecules samples into the slab. It soon became apparent, however, particularly as electrophoresis testing of DNA increased, that it is more convenient and more precise to use precast gel slabs made to uniform composition, size and configuration standards. The most common precast gel slab has a thin planar rectangular shape and includes a series of spaced wells along one or more side walls to receive the biological samples being investigated. Such gel slabs are inherently flimsy and subject to tearing and deformation if not handled gently. A particularly sensitive area is the thin walls separating the sample wells. While any deformation or tearing of the gel slab creates some risk of producing inaccurate tests, a breach between wells allowing commingling of adjacent biological samples would defeat the test purpose. Since the main risk of rough handling occurs during shipping, and the properties of the gel make visual detection of hairline cracks very difficult, it has been found important to protect the gels during shipping.
U.S. Pat. No. 5,443,704 discloses a packaging system for protecting the gel by packaging the gel in a plastic tub, with a foil-lined cover adhered to the top of the tub. In addition to protecting the gel during shipping, the tub can be placed directly into a submarine gel chamber and anchored in place by adhesive strips.
Where precast gel slabs are provided in packaging that cannot be placed in the gel chamber, however, some other means of anchoring the gel slab in a submerged position is required, since the gel nearly the same density as the buffer liquid and will float if it is not anchored. A means that has previously been used to anchor the gel involves a backing sheet adhesively attached to one flat side of the slab. The sheet extends beyond the edges of the slab to form a narrow overhang of sheet along the sides of the slab. A plastic anchor having two long thin beams, connected at the ends and having a thin bridge in the middle, is placed over the slab such that the long beams rest on the sheet overhang. The device is sold under a brand name "Catamaran", possibly because of its appearance. The Catamaran type anchor, however, anchors the backing sheet rather than the gel directly, so that if the gel slab becomes dislodged from the backing sheet when power is switched to the electrodes, the slab will float in the buffer liquid and cause a loss of sample from the wells or skewed electrophoretic patterns. In addition, the plastic backing sheet adhered to the gel precludes transfer of DNA to a solid support such as a nylon membrane, and can make DNA recovery more difficult.
Other than the Catamaran anchor described above, the object frequently used to anchor the bare slab is usually some handy laboratory device selected ad hoc, such as a glass rod or glass plate, and placed across a portion of the slab. While this is a practical solution, it is clearly not optimum, since the laboratory devices often cause distortions in the migration of macromolecules through the gel by interfering with the electrical field.
Consequently, it is an object of this invention to provide a device specifically designed to anchor a precast gel slab in a submarine gel chamber such that the slab does not float on the buffer fluid or become dislodged when electric current is passed between the electrodes. Specific design objectives are that the device anchor the slab by weight alone, rather than by some sort of adhesive or mechanical attachment, so that the anchor can be simply set on top of the gel slab.
Within that overall objective, however, is the consideration that the anchor not cause interference with the electrophoresis process. Consequently, related objectives are that the device have minimal contact with the gel slab, that its weight be evenly distributed over the slab, that the local pressure at the contact points not cause the contact points to lacerate or pierce the slab, and that the anchor provide easy access to the sample wells after it is in place atop the slab. The manner in which these objectives are achieved is described below.